1. Field of the Invention
The technical scope of the invention is that of safety and arming devices for a pyrotechnic train of a projectile and namely micro-machined safety and arming devices.
2. Description of the Related Art
Safety and arming devices (DSA) are well known. They generally incorporate a screen blocking the transmission channel which connects a detonator and pyrotechnic charge.
The screen is thus positioned across the transmission channel of the detonic wave between the detonator and charge and it prevents the latter from functioning.
One of the problems encountered with classical devices is their volume. The parts are relatively massive so as to be able to ensure the interruption of the pyrotechnic train. Motor means enabling the screen to be displaced must therefore be powerful. More often than not it is springs that are used and which remain tensed during the storage phases, which can lead to the deterioration of their mechanical properties and to a reduction in reliability of the armament.
For several years it has been proposed to manufacture all or part of the safety and arming devices using chips incorporating micro-machined or micro-engraved electro-mechanical elements, either in an element deposited on a substrate, or directly on the substrate itself. This technology, known as MEMS (Micro Electra Mechanical System) enables micro-mechanisms to be manufactured implementing a technique similar to that used to produce electronic integrated circuits.
Patent EP2077431 thus discloses a micro-machined safety and arming device in which the arming is fully mechanical and which fulfils the most stringent safety conditions.
Thus, a first lock, or acceleration lock, is released during firing. This lock recoils against the action of a return spring and disengages from a rod integral with the shutter. Once disengaged from the shutter, the first lock is immobilized with respect to the substrate thanks to suitable indentations.
A second lock, or centrifugal lock, is released by the displacement (due to the effect of the projectile's spin) of a counterweight housed in the shutter.
Such a safety and arming device thus enables two independent environmental conditions to be exploited to ensure arming: the longitudinal firing acceleration and the centrifugal acceleration. This double safety enables this device to be compliant with the most stringent standards with respect to projectile arming safety (STANAG 4187).
This safety and arming device nevertheless suffers certain drawbacks.
The first lock in particular (acceleration lock) occupies considerable space in the device. It imposes an increase in the dimensions of the device's substrate and further requires a rod to be provided on the mobile shutter that cooperates with this first lock. In order for the rod not to remain protruding in the pyrotechnic transmission channel in its armed position, it is necessary for the shutter stroke to be extended, thereby further increasing the dimensions of the device.